U.S. patent application number 12/171399 was filed with the patent office on 2008-10-30 for combined gnss gyroscope control system and method.
Invention is credited to Walter J. Feller, John A. McClure, Michael L. Whitehead.
Application Number | 20080269988 12/171399 |
Document ID | / |
Family ID | 41507402 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080269988 |
Kind Code |
A1 |
Feller; Walter J. ; et
al. |
October 30, 2008 |
COMBINED GNSS GYROSCOPE CONTROL SYSTEM AND METHOD
Abstract
A global navigation satellite sensor system (GNSS) and gyroscope
control system for vehicle steering control comprising a GNSS
receiver and antennas at a fixed spacing to determine a vehicle
position, velocity and at least one of a heading angle, a pitch
angle and a roll angle based on carrier phase position differences.
The roll angle facilitates correction of the lateral motion induced
position errors resultant from motion of the antennae as the
vehicle moves based on an offset to ground and the roll angle. The
system also includes a control system configured to receive the
vehicle position, heading, and at least one of roll and pitch, and
configured to generate a steering command to a vehicle steering
system. The system includes gyroscopes for determining system
attitude change with respect to multiple axes for integrating with
GNSS-derived positioning information to determine vehicle position,
velocity, rate-of-turn, attitude and other operating
characteristics. A vehicle control method includes the steps of
computing a position and a heading for the vehicle using GNSS
positioning and a rate gyro for determining vehicle attitude, which
is used for generating a steering command.
Inventors: |
Feller; Walter J.; (Airdrie,
CA) ; Whitehead; Michael L.; (Scottsdale, AZ)
; McClure; John A.; (Scottsdale, AZ) |
Correspondence
Address: |
MARK BROWN
4700 BELLEVIEW SUITE 210
KANSAS CITY
MO
64112
US
|
Family ID: |
41507402 |
Appl. No.: |
12/171399 |
Filed: |
July 11, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10804758 |
Mar 19, 2004 |
7400956 |
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12171399 |
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10828745 |
Apr 21, 2004 |
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10804758 |
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Current U.S.
Class: |
701/41 ;
342/357.36; 342/357.52 |
Current CPC
Class: |
G05D 1/0278 20130101;
G01S 19/14 20130101; A01B 69/007 20130101; G01S 19/53 20130101;
G01S 5/0247 20130101; G05D 1/027 20130101; G01C 21/165 20130101;
G05D 2201/0201 20130101 |
Class at
Publication: |
701/41 |
International
Class: |
B62D 6/00 20060101
B62D006/00 |
Claims
1. A method of controlling a vehicle including a steering control
mechanism, which method comprises the steps of: computing a
position and a heading for the vehicle using a GNSS multiple
antenna system in combination with a rate gyro; computing a
steering control command using said vehicle position and heading;
applying said steering control command to the vehicle steering
mechanism; providing the vehicle steering control mechanism with a
control value corresponding to the performance of the vehicle; and
steering said vehicle with said steering control mechanism
utilizing said steering control command and said control value.
2. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: basing the steering control
command on a first proportionality factor multiplied by a
difference in a desired position versus an actual position plus a
second proportionality factor multiplied by a difference in a
desired heading versus an actual heading; and insuring with said
second proportionality factor that when said vehicle attains said
desired position the vehicle is also directed to said desired
heading, and thereby avoids crossing a desired track.
3. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: using a recursive, adaptive
algorithm to characterize the vehicle response and selected dynamic
characteristics; calculating response times and characteristics for
the vehicle based on said responses; and calibrating said steering
control command by applying a modified steering control command
based on said responses to achieve a desired response.
4. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: providing a wheel velocity
sensor; tracking vehicle wheel velocity with said wheel sensor;
providing a steering direction sensor; monitoring wheel direction
with said steering direction sensor; and providing limits and
assistance in closing adaptive control tracking loops with said
wheel velocity and direction sensors.
5. The method of controlling a vehicle according to claim 4, which
includes the additional steps of: comparing the GNSS-based
velocity, the GNSS-based heading and the rate gyro outputs with the
wheel velocity sensor output and the steering direction sensor
output; and using said output comparisons to model vehicle slippage
and the actual steering rate conditions to enhance the adaptive
control loops.
6. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: providing said vehicle with a
sprayer including multiple spray nozzles or applicators for
applying material to a surface; and applying material using the
rate of change of terrain tilt to adjust spray nozzle or applicator
rates to compensate for terrain tilt.
7. The method of controlling a vehicle according to claim 6, which
includes the additional steps of: varying the rates of application
of the nozzles or applicators based on turn rates calculated by the
gyro and the GNSS receivers to apply the materials at a desired
rate.
8. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: providing the vehicle with a tow
vehicle and an implement connected to the tow vehicle by an
articulated connection; providing said implement with an implement
attitude subsystem including a GNSS receiver and at least two GNSS
antennas spaced apart in a fixed, predetermined relation by a rigid
link; providing said implement attitude subsystem with yaw and roll
gyroscopes adapted for measuring rates of yaw and roll attitude
change for said implement; calculating the implement's attitude
values including tilt, slew, heading, yaw rate and roll rate with
output from said implement GNSS receiver and said gyroscopes; and
correcting the implement's travel path with the vehicle steering
mechanism using said calculated implement attitude values.
9. The method of controlling a vehicle according to claim 8, which
includes the additional steps of: providing said tow vehicle with a
tow vehicle attitude subsystem including a GNSS receiver and at
least two GNSS antennas spaced apart in a fixed, predetermined
relation by a rigid link; providing said tow vehicle attitude
subsystem with yaw and roll gyroscopes adapted for measuring rates
of yaw and roll attitude change for said vehicle; calculating yaw
and roll rates for the tow vehicle with output from said implement
GNSS receiver and gyroscopes; providing said steering control
system with a microprocessor controller; providing output from said
tow vehicle and implement attitude subsystems to said
microprocessor controller; computing steering commands by
integrating said tow vehicle and implement attitude subsystem
outputs; and providing said tow vehicle and implement integrated
steering commands to said steering control mechanism.
10. The method of controlling a vehicle according to claim 1, which
includes the additional steps of: computing vehicle position and
attitude with said GNSS attitude subsystem using measured GNSS
carrier phase differences; providing a yaw gyroscope connected to
said GNSS attitude subsystem; calibrating and initializing said yaw
gyroscope with said GNSS-derived attitude; configuring said yaw
gyroscope to derive and provide an output including a yaw angle and
a yaw angle rate of change and deriving and providing such output;
and using yaw angle and said yaw angle rate of change outputs from
said yaw gyroscope for computing and outputting steering control
commands to the vehicle steering system from the current position
and heading to the desired position and heading.
11. A method of controlling a vehicle including a steering control
mechanism, which method comprises the steps of: computing a
position and a heading for the vehicle using a GNSS multiple
antenna system in combination with a rate gyro; computing a
steering control command; applying selected control values to the
vehicle steering control mechanism; basing the steering control
command on a first proportionality factor multiplied by a
difference in a desired position versus an actual position plus a
second proportionality factor multiplied by a difference in a
desired heading versus an actual heading, said second
proportionality factor insuring that when said vehicle attains said
desired position the vehicle is also directed to said desired
heading, and thereby avoids crossing a desired track; using a
recursive, adaptive algorithm to characterize the vehicle response
and selected dynamic characteristics; calculating response times
and characteristics for the vehicle based on said responses;
calibrating said control commands by applying a modified control
command based on said responses to achieve a desired response;
providing a wheel sensor; tracking vehicle wheel velocity with said
wheel sensor; providing a steering sensor; monitoring wheel
direction with said steering sensor; providing limits and
assistance in closing tracking loops with said wheel velocity and
direction; comparing the GNSS-based velocity and the gyro and
GNSS-based heading with the wheel rate and angle to model the
slippage and the steering rate conditions to enhance the adaptive
control loops; providing said vehicle with a sprayer including
multiple spray nozzles or applicators for applying material to a
surface; applying materials using the rate of change of tilt to
adjust spray nozzle or applicator rates to compensate for roll or
tilt of terrain; and varying the rates of application of the
nozzles or applicators based on turn rates calculated by the gyros
and the GNSS receivers to apply materials in a desired rate.
12. A sensor system for controlling a vehicle steering system,
which sensor system comprises: a global navigation satellite sensor
(GNSS) attitude subsystem including at least one receiver and
multiple antennas connected to said receiver or receivers at a
fixed spacing, said GNSS attitude subsystem computing vehicle
position and attitude using measured GNSS carrier phase
differences; a yaw gyroscope connected to said GNSS attitude
subsystem and configured to derive and provide outputs including
yaw angles and angular rates of change; said yaw gyroscope being
configured for calibration and initialization using said
GNSS-derived attitude; and a steering control subsystem connected
to said yaw gyroscope and said GNSS attitude subsystem and using
said yaw angle and yaw angle rate of change outputs from said yaw
gyroscope for computing and outputting steering control commands to
the vehicle steering system from the current position and heading
to the desired position and heading.
13. The sensor system according to claim 12 wherein said steering
control subsystem is configured for: basing the steering control
command on a first proportionality factor multiplied by a
difference in a desired position versus an actual position plus a
second proportionality factor multiplied by a difference in a
desired heading versus an actual heading; and insuring with said
second proportionality factor that when said vehicle attains said
desired position the vehicle is also directed to said desired
heading, and thereby avoids crossing a desired track.
14. The sensor system according to claim 12, wherein said steering
control subsystem includes: a recursive, adaptive algorithm
characterizing the vehicle response and selected dynamic
characteristics; said steering control subsystem configured for
calculating response times and characteristics for the vehicle
based on said responses; and said steering control subsystem
configured for calibrating said steering control command by
applying a modified steering control command based on said
responses to achieve a desired response.
15. The sensor system according to claim 12, which includes: a
wheel velocity sensor adapted for providing an output corresponding
to wheel velocity; a steering direction sensor adapted for
providing output corresponding to wheel direction; and said
steering control subsystem configured for providing limits and
assistance in closing adaptive control tracking loops with the
output from said wheel velocity and direction sensors.
16. The sensor system according to claim 12 wherein said steering
control subsystem is configured for: comparing the GNSS-based
velocity, the GNSS-based heading and the rate gyro outputs with the
wheel velocity sensor output and the steering direction sensor
output; and using said output comparisons to model vehicle slippage
and the actual steering rate conditions to enhance the adaptive
control loops.
17. The sensor system according to claim 12, which includes: a
function for controlling a sprayer associated with said vehicle and
including multiple spray nozzles or applicators for applying
material to a surface; and said sprayer control function applying
material using the rate of change of terrain tilt to adjust spray
nozzle or applicator rates to compensate for terrain tilt.
18. The sensor system according to claim 12, which includes: said
sprayer control function varying the rates of application of the
nozzles or applicators based on turn rates calculated by the
attitude subsystem to apply the materials at a desired rate.
19. The sensor system according to claim 12, which includes: said
attitude subsystem comprising a tow vehicle attitude subsystem
associated with a tow vehicle; an implement attitude subsystem
associated with an implement connected to the tow vehicle by an
articulated connection; said implement attitude subsystem including
a GNSS receiver and at least two GNSS antennas mounted on said
implement and spaced apart in a fixed, predetermined relation by a
rigid link; said implement attitude subsystem including yaw and
roll gyroscopes adapted for measuring rates of yaw and roll
attitude change or said implement; said implement attitude
subsystem adapted for calculating yaw and roll for the implement
with output from said implement GNSS receiver and gyroscopes; and
said sensor system correcting the implement's travel path with the
vehicle steering mechanism.
20. The sensor system according to claim 12, which includes: said
steering control subsystem including a microprocessor controller;
said tow vehicle and implement attitude subsystems providing output
to said microprocessor controller; said microprocessor controller
computing steering commands by integrating said vehicle and
implement attitude subsystem outputs; and said microprocessor
controller providing said vehicle and implement integrated steering
commands to said steering control mechanism.
21. The sensor system according to claim 12, which includes: an
enclosure adapted for mounting in a fixed, predetermined
orientation on said vehicle; and said GNSS receiver, antennas and
gyroscope being mounted in or on said enclosure.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of and claims the
benefit of: U.S. patent applications Ser. No. 10/804,758, filed
Mar. 19, 2004 and No. 10/828,745, filed Apr. 21, 2004; and U.S.
Provisional Patent Applications No. 60/456,146, filed Mar. 20, 2003
and No. 60/464,756, filed Apr. 23, 2003. This application is
related to U.S. patent application Ser. No. 12/______, filed Jun.
______, 2008. The contents of all of the aforementioned
applications are incorporated by reference herein in their
entireties.
BACKGROUND OF THE INVENTION
[0002] The invention relates generally to automatic guidance
systems and more specifically to a global navigation satellite
system (GNSS) based sensor for vehicle steering control.
[0003] Movable machinery, such as agricultural equipment, open-pit
mining machines, airplane crop dusters and the like all benefit
from accurate global navigation satellite system (GNSS) high
precision survey products, and others. However, in existing
satellite positioning systems (SATPS) for guided parallel and
contour swathing for precision farming, mining, and the like, the
actual curvature of terrain may not be taken into account. This
results in a less than precise production because of the less than
precise parallel or contour swathing. Indeed, in order to provide
swaths through a field (in farming, for example), the guidance
system collects positions of the vehicle as it moves across the
field. When the vehicle commences the next pass through the field,
the guidance system offsets the collected positions for the
previous pass by the width of the equipment (i.e. swath width). The
next set of swath positions is used to provide guidance to the
operator as he or she drives the vehicle through the field.
[0004] The current vehicle location, as compared to the desired
swath location, is provided to the vehicle's operator or to a
vehicle's steering system. The SATPS provides the 3-D location of
signal reception (for instance, the 3-D location of the antenna).
If only 3-D coordinates are collected, the next swath computations
assume a flat terrain offset. However, the position of interest is
often not the same as where the satellite receiver (SR) is located
since the SR is placed in the location for good signal reception,
for example, for a tractor towing an implement, the best location
for the SR may be on top of the cab. However, the position of
interest (POI) for providing guidance to the tractor operator may
be the position on the ground below the operator. If the tractor is
on flat terrain, determining this POI is a simple adjustment to
account for the antenna height.
[0005] However, if the tractor is on an inclined terrain with a
variable tilt, which is often the case, the SATPS alone cannot
determine the terrain tilt so the POI also cannot be determined.
This results in a guidance error because the POI is approximated by
the point of reception (POR), and this approximation worsens as the
terrain inclination increases. This results in cross track position
excursions relative to the vehicle ground track which would
contaminate any attempt to guide to a defined field line or swath.
On inclined terrain, this error can be minimized by collecting the
vehicle tilt configuration along each current pass or the previous
pass. The swath offset thus becomes a vector taking the terrain
inclination into account with the assumption that from the first
swath to the next one the terrain inclination does not change too
much. It can therefore be seen that there is a need for a better
navigation/guidance system for use with a ground-based vehicle that
measures and takes into account vehicle tilt.
[0006] Various navigation systems for ground-based vehicles have
been employed but each includes particular disadvantages. Systems
using Doppler radar will encounter errors with the radar and
latency. Similarly, gyroscopes, which may provide heading, roll, or
pitch measurements, may be deployed as part of an inertial
navigation package, but tend to encounter drift errors and biases
and still require some external attitude measurements for gyroscope
initialization and drift compensation. Gyroscopes have good
short-term characteristics but undesirable long-term
characteristics, especially those gyro copes of lower cost such as
those based on a vibrating resonator. Similarly, inertial systems
employing gyroscopes and accelerometers have good short-term
characteristics but also) suffer from drift. Various systems
include navigating utilizing GNSS; however, these systems also
exhibit disadvantages. Existing GNSS position computations may
include lag times, which may be especially troublesome when, for
example, GNSS velocity is used to derive vehicle heading. As a
result, the position (or heading) solution provided by a GNSS
receiver tells a user where the vehicle was a moment ago, but not
in real time. Existing GNSS systems do not provide high quality
heading information at slower vehicle speeds. Therefore, what is
needed is a low cost sensor system to facilitate vehicle swath
navigation that makes use of the desirable behavior of both GNSS
and inertial units while eliminating or reducing non-desirable
behavior. Specifically, what is needed is a means to employ
low-cost gyroscopes (e.g., micro electromechanical (MEM)
gyroscopes) which exhibit very good short-term low noise and high
accuracy while removing their inherent long-term drift.
BRIEF SUMMARY OF THE INVENTION
[0007] Disclosed herein in an exemplary embodiment is a sensor
system for vehicle steering control comprising: a plurality of
global navigator satellite systems (GNSS) including receivers and
antennas at a fixed spacing to determine a vehicle position,
velocity and at least one of a heading angle, a pitch angle and a
roll angle based on carrier phase corrected real time kinematic
(RTK) position differences. The roll angle facilitates correction
of the lateral motion induced position errors resultant from motion
of the antennae as the vehicle moves based on an offset to ground
and the roll angle. The system also includes a control system
configured to receive the vehicle position, heading, and at least
one of roll, pitch and yaw, and configured to generate a steering
command to a vehicle steering system.
[0008] Also disclosed herein in another exemplary embodiment is a
method for computing a position of a vehicle comprising:
initializing GNSS; computing a first position of a first GNSS
antenna on the vehicle; computing a second position of a second
GNSS antenna; and calculating a heading as a vector perpendicular
to a vector joining the first position and the second position, in
a horizontal plane aligned with the vehicle. The method also
includes computing a roll angle of the vehicle as an arc-tangent of
a ratio of differences in heights of the first GNSS antenna and the
second GNSS antenna divided by a spacing between their respective
phase centers and calculating an actual position at the center of
the vehicle projected to the ground using the computed roll angle
and a known height from the ground of at least one of the first
GNSS antenna and the second GNSS antenna.
[0009] Further disclosed herein in yet another exemplary embodiment
is a method of controlling a vehicle comprising: computing a
position and a heading for the vehicle; computing a steering
control command based on a proportionality factor multiplied by a
difference in a desired position versus an actual position, plus a
second proportionality factor multiplied by a difference in a
desired heading versus an actual heading, the second
proportionality factor ensuring that when the vehicle attains the
desired position the vehicle is also directed to the desired
heading, and thereby avoiding crossing a desired track. The method
also includes a recursive adaptive algorithm employed to
characterize the vehicle response and selected dynamic
characteristics.
[0010] The method further includes applying selected control values
to a vehicle steering control mechanism and measuring responses of
the vehicle thereto; calculating response times and characteristics
for the vehicle based on the responses; and calibrating the control
commands by applying a modified control command based on the
responses to achieve a desired response. Various alternative
aspects and applications of the present invention are disclosed
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 depicts an illustrative diagram of a vehicle
including an exemplary embodiment;
[0012] FIG. 2 depicts an illustrative block diagram of the vehicle
including an exemplary embodiment of a sensor system;
[0013] FIG. 3 depicts an illustrative block diagram of a sensor
system in accordance with an exemplary embodiment;
[0014] FIG. 4 depicts an illustrative sensor system in accordance
with an exemplary embodiment;
[0015] FIG. 5 depicts an illustrative flow chart of an exemplary
process for determining a steering command for a vehicle in
accordance with an exemplary embodiment;
[0016] FIG. 6 depicts an illustrative flow chart of an exemplary
process for determining a steering command with an exemplary sensor
system in accordance with an alternative embodiment;
[0017] FIG. 7A depicts a multi-axis antenna and gyroscope system
embodying an aspect of the present invention and including two
antennas connected by a rigid link and yaw and roll gyroscopes;
[0018] FIG. 7B depicts the system in a yaw attitude;
[0019] FIG. 7C depicts the system in a roll attitude;
[0020] FIG. 8 depicts a tilt (roll) angle measuring application of
the invention on an agricultural vehicle;
[0021] FIG. 9 depicts an alternative aspect of the system with
antenna and gyroscope subsystems mounted on both the vehicle and
the implement, e.g. a sprayer with selectively controllable spray
nozzles; and
[0022] FIG. 10 depicts a block diagram of the system shown in FIG.
9.
DETAILED DESCRIPTION OF THE PREFERRED ASPECTS
[0023] Global navigation satellite systems (GNSS) are broadly
defined to include GPS (U.S.), Galileo (proposed), GLONASS
(Russia), Beidou/Compass (China, proposed), IRNSS (India,
proposed), QZSS (Japan, proposed) and other current and future
positioning technology using signals from satellites, with or
without augmentation from terrestrial sources. Inertial navigation
systems (INS) include gyroscopic (gyro) sensors, accelerometers and
similar technologies for providing output corresponding to the
inertia of moving components in all axes, i.e. through six degrees
of freedom (positive and negative directions along transverse X,
longitudinal Y and vertical Z axes). Yaw, pitch and roll refer to
moving component rotation about the Z, X and Y axes respectively.
Said terminology will include the words specifically mentioned,
derivatives thereof and words of similar meaning.
[0024] Disclosed herein in an exemplary embodiment is a sensor
system for vehicle guidance. The sensor system utilizes a plurality
of GNSS carrier phase differenced antennas to derive attitude
information, herein referred to as a GNSS attitude system.
Moreover, the GNSS attitude system may optionally be combined with
one or more rate gyro(s) used to measure turn, roll or pitch rates
and to further calibrate bias and scale factor errors within these
gyros. In an exemplary embodiment, the rate gyros and GNSS
receiver/antenna are integrated together within the same unit, to
provide multiple mechanisms to characterize a vehicle's motion and
position to make a robust vehicle steering control mechanism.
[0025] It is known in the art that by using a GNSS satellite's
carrier phase, and possibly carrier phases from other satellites,
such as WAAS satellites, a position may readily be determined to
within millimeters. When accomplished with two antennas at a fixed
spacing, an angular rotation may be computed using the position
differences. In an exemplary embodiment, two antennas placed in the
horizontal plane may be employed to compute a heading (rotation
about a vertical Z axis) from a position displacement. It will be
appreciated that an exemplary embodiment may be utilized to compute
not only heading, but either roll (rotation about a longitudinal Y
axis) or pitch (rotation about a lateral X axis) depending on the
orientation of the antennas relative to the vehicle. Heading
information, combined with position, either differentially
corrected (DGPS or DGNSS) or carrier phase corrected real time
kinematic (RTK) provides the feedback information desired for a
proper control of the vehicle direction. Addition of one or more
rate gyros further provides independent measurements of the
vehicle's dynamics and facilitates vehicle steering control. The
combination of GNSS attitude obtained from multiple antennas with
gyroscopes facilitates calibration of gyroscope scale factor and
bias errors which are present in low cost gyroscopes. When these
errors are removed, gyro rates are more accurate and provide better
inputs for guidance and control. Furthermore, gyroscopes can now
effectively be integrated to obtain roll, pitch and heading angles
with occasional adjustment from the GNSS-derived attitude.
[0026] Existing systems for vehicle guidance may employ separate
gyros, and separate GNSS positioning or attitude systems. However,
such systems do not provide an integrated heading sensor based on
GNSS as disclosed herein. Moreover, separate systems exhibit the
limitations of their respective technologies as mentioned earlier.
The exemplary embodiments as described herein eliminate the
requirements of existing systems for other means to correct for
vehicle roll. Moreover, an implementation of an exemplary
embodiment also provides a relatively precise, in both the
short-term and the long-term, means of calculating heading and
heading rate of change (turn rate).
[0027] Another benefit achieved by incorporating a GNSS-based
heading sensor is the elimination or reduction of drift and biases
resultant from a gyro-only or other inertial sensor approach. Yet
another advantage is that heading may be computed while the vehicle
is stopped or moving slowly, which is not possible in a
single-antenna GNSS based approach that requires a vehicle velocity
vector to derive heading. This can be very important in
applications where a vehicle has to turn slowly to align with
another path. During these slow turns the gyro can drift away but
by adding the use of a dual antenna GNSS solution the orientation
of the gyro can be continuously corrected. This also permits
immediate operation of a slow moving vehicle after being at rest,
rather than requiring an initialization from motion. Yet another
advantage of an exemplary embodiment is that a combination of the
aforementioned sensors provides sufficient information for a
feedback control system to be developed, which is standalone and
independent of a vehicle's sensors or additional external sensors.
Thus, such a system is readily maintained as vehicle-independent
and may be moved from one vehicle to another with minimal effort.
Yet another exemplary embodiment of the sensor employs global
navigation satellite system (GNSS) sensors and measurements to
provide accurate, reliable positioning information. GNSS sensors
include, but are not limited to GNSS, Global Navigation System
(GLONAS), Wide Area Augmentation System (WAAS) and the like, as
well as combinations including at least one of the foregoing.
[0028] An example of a GNSS is the Global Positioning System (GPS)
established by the United States government that employs a
constellation of 24 or more satellites in well-defined orbits at an
altitude of approximately 26,500 1km. These satellites continually
transmit microwave L-band radio signals in two frequency bands,
centered at 1575.42 MHz and 1227.6 MHz., denoted as L1 and L2
respectively. These signals include timing patterns relative to the
satellite's onboard precision clock (which is kept synchronized by
a ground station) as well as a navigation message giving the
precise orbital positions of the satellites, an ionosphere model
and other useful information. GNSS receivers process the radio
signals, computing ranges to the GNSS satellites, and by
triangulating these ranges, the GNSS receiver determines its
position and its internal clock error.
[0029] In standalone GNSS systems that determine a receiver's
antenna position coordinates without reference to a nearby
reference receiver, the process of position determination is
subject to errors from a number of sources. These include errors in
the GNSS satellite's clock reference, the location of the orbiting
satellite, ionosphere induced propagation delay errors, and
troposphere refraction errors.
[0030] To overcome the errors of the standalone GNSS system, many
positioning applications have made use of data from multiple GNSS
receivers. Typically, in such applications, a reference receiver,
located at a reference site having known coordinates, receives the
GNSS satellite signals simultaneously with the receipt of signals
by a remote receiver. Depending on the separation distance between
the two GNSS receivers, many of the errors mentioned above will
affect the satellite signals equally for the two receivers. By
taking the difference between signals received both at the
reference site and the remote location, the errors are effectively
eliminated. This facilitates an accurate determination of the
remote receiver's coordinates relative to the reference receiver's
coordinates.
[0031] The technique of differencing signals from two or more GNSS
receivers to improve accuracy is known as differential GNSS (DGNSS
or DGPS). Differential GNSS is well known and exhibits many forms.
In all forms of DGNSS, the positions obtained by the end user's
remote receiver are relative to the position(s) of the reference
receiver(s). GNSS applications have been improved and enhanced by
employing a broader array of satellites such as GNSS and WAAS. For
example, see commonly assigned U.S. Pat. No. 6,469,663 B1 to
Whitehead et al. titled Method and System for GNSS and WAAS Carrier
Phase Measurements for Relative Positioning, dated Oct. 22, 2002,
the disclosures of which are incorporated by reference herein in
their entirety. Additionally, multiple receiver DGNSS has been
enhanced by utilizing a single receiver to perform differential
corrections. For example, see commonly assigned U.S. Pat. No.
6,397,147 B1 to Whitehead titled Relative GNSS Positioning Using a
Single GNSS Receiver with Internally Generated Differential
Correction Terms, dated May 28, 2002, the disclosures of which are
incorporated by reference herein in their entirety.
[0032] Referring now to FIGS. 1 through 4, an illustrative vehicle
10 is depicted including a sensor system 20 in accordance with an
exemplary embodiment. Referring also to FIGS. 2 and 3, block
diagrams of the sensor system 20 are depicted. The sensor system 20
includes, but is not limited to a GNSS attitude system 22,
comprising at least a GNSS receiver 24 and an antenna 26. The GNSS
receiver/antenna systems comprising GNSS attitude system 22
cooperate as a primary receiver system 22a and a secondary receiver
system 22b, with their respective antennas 26a and 26b mounted with
a known separation. The primary receiver system 22a may also be
denoted as a reference or master receiver system, while the
secondary receiver system 22b may also be denoted as a remote or
slave receiver system. It will also be appreciated that the
selection of one receiver as primary versus secondary need not be
of significance; it merely provides a means for distinguishing
between systems, partitioning of functionality, and defining
measurement references to facilitate description. It should be
appreciated that the nomenclature could readily be transposed or
modified without impacting the scope of the disclosure or the
claims.
[0033] The sensor system 20 is optionally configured to be mounted
within a single enclosure 28 to facilitate transportability. In an
exemplary embodiment, the enclosure 28 can be any rigid assembly,
fixture, or structure that causes the antennas 26 to be maintained
in a substantially fixed relative position with respect to one
another. In an exemplary embodiment, the enclosure 28 may be a
lightweight bracket or structure to facilitate mounting of other
components and transportability. Although the enclosure 28 that
constrains the relative location of the two antennas 26a and 26b
may have virtually any position and orientation in space, the two
respective receivers 24 (reference receiver 24a and remote receiver
24b) are configured to facilitate communication with one another
and resolve the attitude information from the phase center of the
reference antenna 26a to the phase center of the remote antenna 26b
with a high degree of accuracy.
[0034] Yet another embodiment employs a GNSS sensor 20 in the
embodiments above augmented with supplementary inertial sensors 30
such as accelerometers, gyroscopes, or an attitude heading
reference system. More particularly, in an implementation of an
exemplary embodiment, one or more rate gyro(s) are integrated with
the GNSS sensor 20.
[0035] In yet another exemplary embodiment, a gyro that measures
roll-rate may also be combined with this system's GNSS-based roll
determination. A roll rate gyro denoted 30b would provide improved
short-term dynamic rate information to gain additional improvements
when computing the sway of the vehicle 10, particularly when
traveling over uneven terrain.
[0036] It will be appreciated that to supplement the embodiments
disclosed herein, the data used by each GNSS receiver 24 may be
coupled with data from supplementary sensors 50, including, but not
limited to, accelerometers, gyroscopic sensors, compasses, magnetic
sensors, inclinometers, and the like, as well as combinations
including at least one of the foregoing. Coupling GNSS data with
measurement information from supplementary sensors 30, and/or
correction data for differential correction improves positioning
accuracy, improves initialization durations and enhances the
ability to recover for data outages. Moreover, such coupling may
further improve, e.g., reduce, the length of time required to solve
for accurate attitude data.
[0037] It will be appreciated that although not a requirement, the
location of the reference antenna 26a can be considered a fixed
distance from the remote antenna 26b. This constraint may be
applied to the azimuth determination processes in order to reduce
the time required to solve for accurate azimuth, even though both
antennas 26a and 26b may be moving in space or not at a known
location. The technique of resolving the attitude information and
position information for the vehicle 10 may employ carrier phase
DGNSS techniques with a moving reference station. Additionally, the
use of data from auxiliary dynamic sensors aids the development of
a heading solution by applying other constraints, including a rough
indication of antenna orientation relative to the Earth's gravity
field and/or alignment to the Earth's magnetic field.
[0038] Producing an accurate attitude from the use of two or more
GNSS receiver and antenna systems 22 has been established in the
art and therefore will not be expounded upon herein. The processing
is utilized herein as part of the process required to implement an
exemplary embodiment.
[0039] Referring also to FIG. 4, a mechanism for ensuring an
accurate orientation of the sensor system 20 to the vehicle 10 may
be provided for by an optional mounting base 14 accurately attached
to the enclosure 28. An accurate installation ensures that
substantially no misalignment error is present that may otherwise
cause the sensor system 20 to provide erroneous heading
information. The mounting base 14 is configured such that it fits
securely with a determinable orientation relative to the vehicle
10. In an exemplary embodiment, for example, the mounting base 14
is configured to fit flatly against the top surfaces of the vehicle
10 to facilitate an unimpeded view to the GNSS satellites.
[0040] With the sensor system 20 affixed and secured in the vehicle
10 power up and initialization of the sensor system 20 is
thereafter executed. Such an initialization may include, but not be
limited to, using the control system 100 to perform any
initialization or configuration that may be necessary for a
particular installation, including the configuration of an internal
log file within the memory of the sensor system 20.
[0041] The sensor system 20 may further include additional
associated electronics and hardware. For example, the sensor system
20 may also include a power source 32, e.g., battery, or other
power generation means, e.g., photovoltaic cells, and ultrahigh
capacity capacitors and the like. Moreover, the sensor system 20
may further include a control system 100. The control system 100
may include, without limitation, a controller/computer 102, a
display 104 and an input device 106, such as a keypad or keyboard
for operation of the control system 100. The controller 102 may
include, without limitation, a computer or processor, logic,
memory, storage, registers, timing, interrupts, input/output signal
interfaces, and communication interfaces as required to perform the
processing and operations prescribed herein. The controller
preferably receives inputs from various systems and sensor elements
of the sensor system 20 (GNSS, inertial, etc.), and generates
output signals to control the same and direct the vehicle 10. For
example, the controller 102 may receive such inputs as the GNSS
satellite and receiver data and status, inertial system data, and
the like from various sensors. In an exemplary embodiment, the
control system 100 computes and outputs a cross-track and/or a
direction error relating to the current orientation, attitude, and
velocity of the vehicle 10 as well as computing a desired swath on
the ground. The control system 100 will also allow the operator to
configure the various settings of the sensor system 20 and monitor
GNSS signal reception and any other sensors of the sensor system
20. In an exemplary embodiment, the sensor system 20 is
self-contained. The control system 100, electronics, receivers 24,
antennas 26, and any other sensors, including an optional power
source, are contained within the enclosure 12 to facilitate ease of
manipulation, transportability, and operation.
[0042] Referring now to FIG. 5, a flowchart diagrammatically
depicting an exemplary methodology for executing a control process
200 is provided. An exemplary control process 200, such as may be
executed by an operator in conjunction with a control system 100,
acts upon information from the sensor system 20 to output
cross-track and/or direction error based upon corrected 3-D
position, velocity, heading, tilt, heading rate (degrees per
second), radius of curvature and the like.
[0043] System 22a computes its position, denoted p.sub.1(x.sub.1,
y.sub.1, z.sub.1). Referring now to block 220, the secondary
receiver and antenna system 22b computes its position, denoted
p.sub.2 (x.sub.2, y.sub.2, z.sub.2). Referring now to block 230,
optionally additional receiver and antenna system(s) 22 compute
their respective positions, denoted p.sub.3(x.sub.3, y.sub.3,
z.sub.3), . . . p.sub.n(x.sub.n, y.sub.n, z.sub.n).
[0044] At process block 240, employing a geometric calculation the
heading is computed as the vector perpendicular to the vector
joining the two positions, in the horizontal plane (assuming they
are aligned with the vehicle 10). Furthermore, at block 250 the
roll of the vehicle 10 may readily be computed as the arc-tangent
of the ratio of the difference in heights of the two antennas 26a
and 26b divided by the spacing between n their phase centers (a
selected distance within the enclosure 12). It will be appreciated
that optionally, if additional receiver and antenna systems are
utilized and configured for additional measurements, the pitch and
roll angles may also be computed using differential positioning
similar to the manner for computing heading. Therefore, in FIG. 5,
optionally at process block 260, the pitch and roll may be
computed.
[0045] Continuing with FIG. 5, at process block 270, using the
computed roll angle and a known antenna height (based on the
installation in a given vehicle 10), the actual position at the
center of the vehicle 10 projected to the ground may be calculated.
This position represents a true ground position of the vehicle 10.
Once the ground position is known, the error value representing the
difference between where the vehicle should be based on a computed
swath or track, and where it actually is, can be readily calculated
as shown at block 280.
[0046] Optionally, the vector velocities of the vehicle 10 are also
known or readily computed based on an existing course and heading
of the vehicle 10. These vector velocities may readily be utilized
for control and instrumentation tasks.
[0047] Turning now to FIG. 6, in another exemplary embodiment a
steering control process 300 can utilize the abovementioned
information from the sensor system 20 to direct the vehicle motion.
At process block 310 the steering control may be initiated by
obtaining the computed errors from process 200. Turning to block
320, the steering control process 300 may be facilitated by
computing a steering control command based on a proportionality
factor times the difference in desired position versus actual
position (computed position error), plus a second proportionality
factor times the difference in desired heading versus actual
heading (heading error). The second proportionality factor ensures
that when the vehicle attains the desired position it is actually
directed to the correct heading, rather than crossing the track.
Such an approach will dramatically improve steering response and
stability. At process block 330, a steering command is generated
and directed to the vehicle 10.
[0048] Moreover, continuing with FIG. 6, optionally a recursive
adaptive algorithm may also be employed to characterize the vehicle
response and selected dynamic characteristics. In an exemplary
embodiment, the sensor system 20 applies selected control values to
the vehicle steering control mechanism as depicted at optional
block 340 and block 330. The sensor system 20 measures the response
of the vehicle 10 as depicted at process block 350 and calculates
the response times and characteristics for the vehicle. For
example, a selected command is applied and the proportionality of
the turn is measured given the selected change in steering. Turning
to process block 360, the responses of the vehicle 10 are then
utilized to calibrate the control commands applying a modified
control command to achieve a desired response. It will be
appreciated that such an auto-calibration feature would possibly be
limited by constraints of the vehicle to avoid excess stress or
damage as depicted at 370.
[0049] It will be appreciated that while a particular series of
steps or procedures is described as part of the abovementioned
alignment process, no order of steps should necessarily be inferred
from the order of presentation. For example, the process 200
includes installation and power up or initialization. It should be
evident that power-up and initialization could potentially be
performed and executed in advance without impacting the methodology
disclosed herein or the scope of the claims.
[0050] It should further be appreciated that while an exemplary
partitioning functionality has been provided, it should be apparent
to one skilled in the art that the partitioning could be different.
For example, the control of the primary receiver 24a and the
secondary receiver 24b, as well as the functions of the controller
102, could be integrated in other units. The processes for
determining the alignment may, for ease of implementation, be
integrated into a single receiver. Such configuration variances
should be considered equivalent and within the scope of the
disclosure and claims herein.
[0051] The disclosed invention may be embodied in the form of
computer-implemented processes and apparatuses for practicing those
processes. The present invention can also be embodied in the form
of computer program code containing instructions embodied in
tangible media, such as floppy diskettes, CD-ROMs, hard drives, or
any other computer-readable storage medium 80 wherein the computer
becomes an apparatus for practicing the invention when the computer
program code is loaded into and executed by the computer. The
present invention can also be embodied in the form of computer
program code stored in a storage medium or loaded into and/or
executed by a computer, for example. The present invention can also
be embodied in the form of a data signal 82 transmitted by a
modulated or unmodulated carrier wave, over a transmission medium,
such as electrical wiring or cabling, through fiber optics or via
electromagnetic radiation. When the computer program code is loaded
into and executed by a computer, the computer becomes an apparatus
for practicing the invention. When implemented on a general-purpose
microprocessor, the computer program code segments configure the
microprocessor to create specific logic circuits.
[0052] FIG. 7A shows another alternative aspect of the invention
including a GNSS antenna and gyroscope attitude system 402 with
antennas 405, 406 separated by a rigid link 407. In a typical
application, the rigid link 407 is attached to the vehicle 10 and
extends along the X (transverse) axis or transversely with respect
to the vehicle's direction of travel, which generally corresponds
to the Y (heading) axis. Alternatively, the vehicle 10 itself can
provide the rigid link between the antennas 405, 406, for example,
by mounting the antennas 405, 406 at predetermined, fixed locations
on the roof of the vehicle cab with a predetermined, fixed distance
therebetween. Another alternative is to provide a GNSS attitude
device with antennas, receivers and sensors (e.g., gyroscopes
(gyros), accelerometers and other sensors) in a self-contained,
unitary enclosure, such as the device 20 shown in enclosure 28 in
FIG. 4. Regardless of the antenna-mounting structure, the
orientation of the antenna pair and the rigid link 407 (or vehicle
10) is determined with respect to an Earth-fixed coordinate system.
The XYZ axes shown in FIG. 7A provide an example for defining this
relation. Roll and yaw gyros 430, 440 are generally aligned with
the Y and Z axes respectively for detecting and measuring vehicle
10 attitude changes with respect to these axes.
[0053] With the system 402 installed on a vehicle 10 (FIG. 8), the
two antennas 405, 406 can provide angular orientations with respect
to two axes. In the example shown, angular orientation with respect
to the Y (heading) axis corresponds to vehicle roll and with
respect to the Z (vertical) axis corresponds to vehicle yaw. These
orientations are commonly of interest in agricultural vehicles
whereby this is the preferred mounting and orientation arrangement
for such applications. The vehicle's roll most adversely affects
GNSS-measured vehicle cross-track error. By measuring the vehicle's
roll, such cross-track errors can be compensated for or eliminated.
Such roll-induced cross-track errors include variable roll errors
due to uneven terrain and constant roll errors due to hill slopes.
It will be appreciated that adding a third antenna provides
three-axis (XYZ) attitude solutions corresponding to pitch, roll
and yaw. Of course, reorienting the two-antenna system 402 can
provide other attitude solutions. For example, locating the
antennas' baseline (aligned with the rigid link 407) fore-and-aft
along the vehicle's Y axis will provide pitch and yaw
attitudes.
[0054] FIG. 7B shows the system 402 in a yaw attitude or condition
whereby the vehicle 10 has deviated from a desired heading along
the Y axis to an actual heading by a yaw angle .theta..sub.Y. In
other words, the vehicle 10 has rotated (yawed) clockwise with
respect to the Z axis. FIG. 7C shows the system 402 in a roll
attitude or condition whereby the vehicle 10 has deviated from
level to a tilt or roll angle of .theta..sub.R. In other words, the
vehicle 10 has rotated (rolled) counterclockwise with respect to
the Y axis.
[0055] The system 402 includes roll and yaw gyros 430, 440 mounted
and oriented for detecting vehicle rotational movement with respect
to the Y and Z axes. The system 402 represents a typical strap-down
implementation with the vehicle 10, antennas 405, 406 and gyros
430, 440 rigidly connected and moving together. A body-fixed
coordinate system is thus defined with the three perpendicular axes
XYZ.
[0056] In all but the most extreme farmlands, the vehicle 10 would
normally deviate relatively little from level and horizontal,
usually less than 30.degree. in most agricultural operations. This
simplifies the process of calibrating the gyros 430, 440 using the
GNSS attitude system 402 consisting of two or more antennas 405,
406. For simplicity, it is assumed that the body-fixed axes XYZ
remain relatively close to level. Thus, the change in the heading
(yaw) angle .theta..sub.Y of FIG. 7B is approximately measured by
the body-fixed yaw gyro 440, even though there may be some small
discrepancy between the axes of rotation. Similar assumptions can
be made for the roll angle .theta..sub.R (FIG. 7C), which is
approximately measured by the body-fixed roll gyro 430. A similar
assumption could be used for measuring pitch attitude or
orientation angles with a pitch gyro.
[0057] This simplifying assumption allows the gyros to be decoupled
from one another during integration and avoids the necessity of
using a full strap-down quaternion implementation. For example,
heading deviation is assigned only to the yaw gyro 440 (gyro axis
perturbations from the assumed level axis alignment are ignored).
Similarly, vehicle roll is assumed to be measured completely by a
single roll gyro 430. GNSS attitude-measured heading and roll can
then be used to calibrate the gyros 430, 440. Such simplifying
assumptions tend to be relatively effective, particularly for
agricultural operations on relatively flat, level terrain.
Alternatively, a full six-degrees-of-freedom strap-down gyro
implementation with quaternion integration could be employed, but
such a solution would normally be excessive and represent an
ineffective use of computing resources, unless an inertial
navigation system (INS) was also being used to backup GNSS, for
example, in the event of GNSS signal loss.
[0058] For the purpose of calibrating the gyroscopes 430, 440, the
angles measured by the GNSS attitude system 402 are used as truth
in a Kalman filter estimator of gyro bias and scale factor errors.
Over a small interval of time, T, the following equation holds:
{dot over (.theta.)}.sub.gyroT=A.theta..sub.true+BT
Where
[0059] {dot over (.theta.)}.sub.gyro=average gyro reading over
[0059] T = 1 / n n .theta. . gyro ##EQU00001##
(with n readings taken over time T) [0060] {dot over
(.theta.)}.sub.gyro=truth angular change over interval T as
measured by the GNSS attitude system. [0061] A=gyro scale factor
error [0062] B=gyro rate bias error
[0063] A two state Kalman filter is defined to have the gyro rate
basis and scale factor error as states. The Kalman process model is
a first-order Markov:
X k + 1 = [ 1 0 0 1 ] X k + [ .sigma. A 0 0 .sigma. B ] W k
##EQU00002##
where the state vector X=[A B] Here .sigma..sub.A and .sigma..sub.B
are noise amplitudes and W is white noise. This dictates what is
known as a random walk of the state [A B]. The designer of the
Kalman filter chooses .sigma..sub.A and .sigma..sub.B according to
how rapidly the bias and scale factor errors are expected to vary
(usually variations due to temperature dependencies of scale and
bias in a low cost gyro). Typical variations, especially of the
scale factor, are quite small (A and B are nearly constant), and
.sigma..sub.A and .sigma..sub.B are chosen accordingly. Typical
values for a low-cost gyroscope, using a time interval T are:
.sigma. A = 0.02 T 1200 , .sigma. B = T 1200 ##EQU00003##
where T is expressed in seconds and 1200 means 1200 seconds. For
example, here the random walk is chosen to cause a drift in scale
factor of 0.02 in 1200 seconds. The Kalman measurement equation is:
[0064] y=Hx+v
Where
[0064] [0065] y= {dot over (.theta.)}.sub.gyroT,
H=[.theta..sub.gyroT] and v is measurement noise. The Kalman
covariance propagation and gain calculation is designed according
to well-known techniques.
[0066] Similar Kalman filters are deployed in both yaw and roll
(and/or pitch) channels. The GNSS attitude devices 20 provides a
reference yaw and roll that act as the Kalman measurements enabling
the calibration of gyro rate basis and scale factor errors. The
GNSS device provides heading and roll, even when the vehicle is
stationary or traveling in reverse. This provides a significant
advantage over single-antenna systems which provide a vehicle
direction only when moving (i.e., a velocity vector). The
multi-antenna attitude device 20 enables continuous calibration
regardless of whether or not and in what direction the vehicle 10
is moving.
[0067] The calibrated gyros 430, 440 are highly advantageous in a
vehicle steering control system. High precision heading and
heading-rate produced by the calibrated yaw gyro is a very accurate
and instantaneous feedback to the control of vehicle changes in
direction. The angular rate produced by the gyro is at least an
order of magnitude more accurate than the angular rate produced by
pure GNSS systems, even those with multiple antennas. The system
402 is also very responsive. The feedback control needs such
relatively high accuracy and responsiveness in heading and
heading-rate to maintain control loop stability. It is well known
that rate feedback in a control loop enhances stability. On a farm
vehicle, where vehicle dynamics may not be fully known or modeled,
this aspect is particularly important. The rate term allows a
generic control system to be developed which is fairly insensitive
to un-modeled vehicle dynamics. A relatively accurate heading and
heading-rate-of-turn can be calculated for use in a vehicle
automatic steering system.
[0068] Another advantage of the system 402 is that a gyro
calibrated to measure tilt angle can provide the vehicle's tilt
much more accurately than a system relying exclusively on GNSS
positioning signals. This advantage is particularly important in
high-precision autosteering, e.g., to the centimeter level. Errors
in GNSS attitude are effectively increased by the ratio of the
antenna spacing to the mounted height of the antennas above the
ground, as illustrated in FIG. 8, which shows an attitude system
402 comprising a pair of antennas 405, 406 connected by a link 407,
as described above. The system 402 is shown tilted through a tilt
(roll) angle .theta..sub.R. An imaginary antenna height line
perpendicular to the rigid link 407 is projected to the "true"
ground position of the vehicle 10 in FIG. 8 and forms the roll
angle with respect to the Z axis. The relative antenna height
differential can be projected along the vertical Z axis to a ground
intercept point and establishes a cross-track error (distance
between the vehicle true ground position and the Z axis ground
intercept point), whereby errors in the antenna height differential
are amplified by the ratio of the rigid link 407 length to the
antenna height. The spacing of the antennas 405, 406, which
corresponds to the length of the rigid link 407, is typically
limited by the width of the vehicle 10, which can be relatively
tall, thereby resulting in a relatively large antenna
height-to-spacing ratio, e.g., five-to-one. Furthermore,
noise-induced errors present in GNSS relative antenna height
differentials (e.g., carrier phase noise, etc.) will be multiplied
by this ratio, which can cause steering errors, including steering
oscillations, etc.
[0069] The GNSS attitude system 402 utilizes a roll gyro (e.g.,
430) for measuring rate-of-change of the roll angle, rather than
the absolute roll angle, which rate of change is integrated to
compute absolute roll angle. The constant of integration can be
initialized to the current GNSS-derived roll angle and then
subsequently steered to the GNSS roll angle by filtering with a
Hatch filter or similar filter used for smoothing the code phase
against the carrier phase in the GNSS receivers. Relatively smooth
vehicle roll estimates can thus be achieved with a gyro.
[0070] More specifically, in an exemplary embodiment, the filtering
is supplemented by the equation:
.theta..sub.filter(k)=.DELTA..sub.gyro(k)+Gain*[.theta..sub.GNSS(k)-.the-
ta..sub.filter(k-1)-.DELTA..sub.gyro(k)]
.DELTA..sub.gyro(k)=.theta..sub.gyro(k)-.theta..sub.gyro(k-1)
Where .theta..sub.filter(k) is the desired output roll angle (at
time k) smoothed by gyro roll angle, but steered to GNSS roll
angle. The GNSS roll (at time k) is .theta..sub.GNSS(k) while the
raw gyro angular reading is .theta..sub.gyro(k) which is obtained
by integrating gyro angular rate. The difference in gyro integrated
rate over one time interval (k-1 to k) is denoted
.DELTA..sub.gyro(k). The filter bandwidth and weighting of the GNSS
roll angle into the solution is set by the filter's gain (denoted
Gain). One method to choose the gain is to assign Gain=T/.tau.
where T is the time span from epoch to epoch and .tau. is a
time-constant, typically much larger than T. The smaller the Gain,
the less the GNSS roll angle is weighted into the solution. The
gain is chosen to give a smooth filtered roll output, dominated by
the low gyro noise characteristics, but also maintaining alignment
with GNSS roll. Since the gyro is calibrated in terms of its scale
and bias errors per the methods described earlier, the gain can be
chosen to be very small (much less than 1) and still the filtered
roll angle closely follows the GNSS roll angle, but without the
noise of the GNSS derived roll angle. Similar schemes can be
deployed for pitch and heading angles if needed, all with the
benefit of improved steering if such angles are used in the
steering control feedback.
[0071] FIG. 9 shows a GNSS and gyroscopic control system 502
comprising an alternative aspect of the present invention in a
tractor and sprayer agricultural equipment application 504. The
vehicle (e.g., a motive component or tractor) 10 is connected to a
working component (e.g., a sprayer) 506 by an articulated
connection 508, which can comprise a conventional tongue-and-hitch
connection, or a powered, implement steering system or hitch, such
as those shown in U.S. Pat. No. 6,865,465, No. 7,162,348 and No.
7,373,231, which are assigned to a common assignee herewith and are
incorporated herein by reference.
[0072] The tractor 10 and the sprayer 506 mount tractor and sprayer
GNSS antenna and gyroscope attitude subsystems 510, 512
respectively, which are similar to the system 402 described above
and provide GNSS-derived position and attitude outputs,
supplemented by gyro-derived rate of rotation outputs for
integration by the control system 502. The sprayer 506 includes a
spray boom 514 with multiple nozzles 516 providing spray patterns
518 as shown, which effectively cover a swath 520. The system 502
can be programmed for selectively controlling the nozzles 516. For
example, a no-spray area 522 is shown in FIG. 9 and can comprise,
for example, an area previously sprayed or an area requiring spray.
Based on the location of the no-spray area 522 in relation to the
spray boom 514, one or more of the nozzles 516 can be selectively
turned on/off. Alternatively, selective controls can be provided
for other equipment, such as agricultural planters wherein the seed
boxes can be selectively turned on/off.
[0073] FIG. 10 shows some of the major components of the system
502, including the GNSS antenna and gyroscope attitude subsystems
510, 512 with antennas 405, 406 separated by rigid links 407, as
described above, and inertial gyros 514. The tractor and implement
10, 506 can be equipped with comparable systems including DGNSS
receivers 524, suitable microprocessors 526 and the inertial gyros
529. Additional sensors 528 can include wheel counters, wheel turn
sensors, accelerometers, etc. The system components can be
interconnected by a CAN connection 530. Alternatively, components
can be wirelessly interconnected, e.g., with RF transmitters and
receivers.
[0074] In operation, the functions described above can be
implemented with the system 502, which has the additional advantage
of providing GNSS and gyro-derived positioning and attitude signals
independently from the tractor 10 and the implement 506. Such
signals can be integrated by one or both of the microprocessors
526. The tractor 10 can be automatically steered accordingly
whereby the implement 506 is maintained on course, with the
additional feature of selective, automatic control of the nozzles
516. For example, FIG. 9 shows the course of the tractor 10
slightly offset to the course of the sprayer 516, which condition
could be caused by a downward left-to-right field slope. Such
sloping field conditions generate roll attitudes, which could also
be compensated for as described above. For example, the system 502
can adjust the output from the spray nozzles 516 to compensate for
such variable operating conditions as sloping terrain, turning
rates, tire slippage, system responsiveness and field
irregularities whereby the material is uniformly applied to the
entire surface area of the field. Moreover, the GNSS-derived
positioning and heading information can be compared to actual
positioning and heading information derived from other sensors,
including gyros, for further calibration.
[0075] While the description has been made with reference to
exemplary embodiments, it will be understood by those of ordinary
skill in the pertinent art that various changes may be made and
equivalents may be substituted for the elements thereof without
departing from the scope of the disclosure. In addition, numerous
modifications may be made to adapt the teachings of the disclosure
to a particular object or situation without departing from the
essential scope thereof. Therefore, it is intended that the claims
not be limited to the particular embodiments disclosed as the
currently preferred best modes contemplated for carrying out the
teachings herein, but that the claims shall cover all embodiments
falling within the true scope and spirit of the disclosure.
* * * * *